Fibrous board products of improved surfaces and process



3,485,714 FIBROUS BOARD PRODUCTS F IMPROVED SURFACES AND PROCESS Kendall D. White, J12, Palatine, llll., assignor to United States Gypsum Company, Chicago, Ill., a corporation of Delaware No Drawing. Filed July 19, 1966, Ser. No. 566,228 Int. Cl. D21h 1/10 U.S. Cl. 16Z-201 6 Claims ABSTRACT 0F THE DISCLOSURE A mat of cooked lignocellulose materials having dry water-soluble materials collected on at least one surface portion thereof is immersed in water at a temperature of at least 140 F. Excess Water is removed following such immersion and the mat is quickly dried at a temperature in excess of 275 F. Said immersion and rapid drying distributing a portion of said water-soluble materials in the body of said mat.

This invention relates to fibrous board products having improved surfaces and a process for their manufacture, and more particularly to improvements in the surface characteristics of dense lignocellulosic sheets such as a hardboard.

When a lignocellulose material such as wood chips is partially cooked with water or steam, either with or without certain chemicals such as sodium carbonate, sodium hydroxide, etc. a substantial amount of water-soluble materials such as sugars, salts, acidic materials, etc. are formed. Unless the chips or fibers are subjected to a vigorous washing operation, the water-soluble materials are distributed among the fibers when they are formed into a sheet or a mat such as for pressing into hardboard. These water-soluble materials, plus those which are added from the size and the make up water, collect upon the surface of the hardboard mat during drying in areas of irregular concentration, and when the mat is subsequently pressed with heat to form a hardboard, the surface sometimes sticks to the press platen or caul plate. This not only results in an undesirable surface upon the hardboard but also the hardboard is difficult to remove from the press. Even if there is no sticking the irregular concentration of the water-soluble materials upon the hardboard surface sometimes results in a mottled appearance.

The preparation of a hardboard is Well known in the art. Some are prepared following the method described in one or more of U.S. Patent Nos. 2,215,244, 2,234,126 and 2,388,487. Briefly, the process consists of forming a mat of natural or partially cooked lignocellulose fibers as a pulp, usually containing size and/or drying oils precipitated with an acidic precipitant such as ferric sulfate, upon a Fourdrinier or cylinder machine. The mats are substantially bone dried and then pressed to a density of at least 45 lbs/cu. ft. with heat at a temperature of over 400 F., usually around 470 F. to 500 F.

Various means have been resorted to in the past to remove these undesirable water-soluble materials from the surface of the mat before pressing into a hardboard. U.S. Patent No. 2,317,394 removes the water-soluble material by washing the pulp prior to formation into a mat, while U.S. Patent Nos. 2,356,285 and 2,802,403 remove the water-soluble material by applying fresh water to the surface of the wet mat prior to drying and drawing it entirely through to the other side by means of a pressure difference. U.S. Patent No. 2,880,655 removes the entire surface of the mat inasmuch as the offending water-soluble materials are concentrated therein and U.S. Patent No. 2,888,376 heats the surface of the mat to a temperature above 400 F. to destroy the stickuitcd States Patent (3 ing properties of the water-soluble materials. All of the above methods are expensive and if a more simplified operation could be developed a marked advance in the art would ensue.

This invention sets forth a novel and simplified process by which an improved hardboard having a smooth unmottled surface can be pressed without sticking from a mat formed from lignocellulose fibers having an irregular concentration of water-soluble materials upon its surface by merely adding a small amount of water to the surface of the mat followed by drying in a manner which will be subsequently described in detail.

It is therefore an object of this invention to provide a fibrous board product which has the water-soluble materials upon at least one surface substantially evenly distributed throughout the surface area.

Ityis an added object of this invention to provide a means by which water-soluble materials are evenly distributed over the entire surface area of a fibrous board product.

It is a further object of this invention to provide an improved hardboard containing partially cooked lignocellulosic fibers with water-soluble materials within its surface area without surface blemishes due to sticking or mottling.

It is also an object of this invention to provide an improved method of evenly distributed water-soluble materials which have collected upon the surface of a hardboard mat throughout the surface area thereof prior to pressing.

It is a still further object of this invention to provide a method of producing a hardboard under high heat and pressure without sticking from a mat containing partially cooked wood fibers and an irregular concentration of water-soluble materials upon its surface.

Various other objects will readily occur to those skilled in the art of which this invention is a part.

The objects of this invention are accomplished by a novel treatment of at least one of the surfaces of a fibrous board product which has water'soluble materials deposited in areas of irregular concentration thereon such that the water-soluble materials are uniformly distributed throughout the entire surface area. A specific example of such a fibrous board product is a mat used in the preparation of hardboard. Following this invention, the water-soluble materials upon the surface of the mat are uniformly distributed over the entire surface area by the application of hot water over the surface. This, along with a short penetration into the body of the mat, results in a uniform distribution of the watersoluble materials over the entire surface area. This is followed by a removal of the water by heat evaporation before the water-soluble materials have a chance to recollect upon the surface to cause sticking and mottling. The concentration at the surface is now such that sticking and mottling is no longer a source of trouble. This operation can be very simply carried out as will be shown in the following examples.

EXAMPLE 1 A series of hardboard mats from cooked hardwoods and containing a substantial quantity of dry water-soluble materials collected in areas of irregular concentration upon their surfaces was passed end to end in a continuous manner into a shallow pool of water heated to a temperature of F. The time of each mat in the pool was between 3 to 4 seconds. A roller was used to remove any surplus water which may have collected upon the mat surface upon emergence from the pool. The mats were then placed upon pallets and taken to the predryer where they were loaded into cars and passed therethrough and the surfaces quickly dried at a temperature of about 330 F. After the mats were dried, they were then pressed in the normal manner, i.e. at a temperature of about 490 F. for about 2 minutes. There was no mottling upon the surface of the hardboard or sticking of the board in the press. Obviously some of the water-soluble materials are removed by the water in the pool. While it is possible to permit a build up of such dissolved materials in the pool water and still have an effective treatment it is preferred to use as fresh a Water as possible and not merely depend upon the addition of fresh make up water to compensate for that removed with the mats.

EXAMPLE 2 Another method which is less effective than that of Example No. 1 and adapted to plant operation is to apply hot water at about 190 F. to the mat immediately upon emerging from the dryer and before stacking, preferably before slitting, immediately followed by the removal of a substantial portion of the water by evaporation such as by heating with a hot ironing roll or direct contact with a flame. If the mats are to be placed into the predryer for the formation of hardboard shortly after the application of hot water the remaining or all of the water can be removed therein.

It is not the intention to limit the scope of this invention to the examples set forth above for the water can be added by any other means such for example as by spraying. The drying can also be carried out by means other than that set forth above. Nor is it the intention to limit the scope of this invention to hardboard mats as other fibrous board products having a problem of irregular concentration of water-soluble materials upon the surface can be similarly treated.

Regardless of the method used, it is important that at least about 16 lbs. of the 190 F. water and preferably more such as 25 to 35 lbs. be evenly distributed over each 1000 sq. ft. of the fibrous board product to be treated in order to have an effective uniform distribution; a mere wetting of the surface is insufficient. However, water should not be standing in pools upon the board surface when it reaches the dryer. In determining the amount of water needed allowance must be made for the extra water which may penetrate into the board along the edges and ends when it is passed through a pool as in the above Example 1.

The temperature of the fresh Water can be varied above and below the 190 F. used in the example. A much higher temperature is close to that of the boiling point of water and is not as easily used. The lowest temperature is that which will just overcome the resistance to penetration by water caused by the size or other added material so that the water can rapidly penetrate into the mat and effect a uniform distribution of the watersoluble materials. For a hardboard mat containing tall oil and tung oil with ferric sulfate used as a precipitant the lowest water temperature is about 140 F. It is evident that the time required for the water to penetrate sufiiciently into the body of the mat and hence the time of treatment is determined to a certain extent by the temperature of the fresh water and the type and amount of size or oil contained in the mat. The treating time may vary from about 2 seconds to as much as about 20 seconds and the penetration from about .005" to .020". Obviously a longer time and a greater penetration can be followed but such will ordinarily result in greater operating difficulty with questionable benefit.

The drying temperature should be suflicient to remove the water by evaporation in such a manner that there is not reconcentration in areas upon the surface. A temperature of over about 275 F. is preferred. It has been found that when the water has been removed before a storage time of 24 hours that satisfactory results can be obtained. A longer time will probably not be undesirable, however, it was found that mats treated following Example 1 and stacked with the surfaces wet for 2 weeks without drying caused sticking when pressed after all moisture was removed.

While the exact process by which the water-soluble materials are prevented from causing clinging or sticking during pressing, as well as mottling, is not entirely clear, it is believed that such is due to the added water carrying with it the water-soluble materials over and into the mat thereby removing the highly concentrated darkened spots and distributing the water-soluble materials evenly over the entire surface area so that the concentration is reduced sufficiently so that sticking will not occur and mottling is prevented by the uniform distribtuion of the dissolved materials.

The offending water-soluble materials can consist of sugars and other water-soluble by-products from the cooking of the lignocellulose, sizing materials and the solubles in the make-up water. Some of these are acidic and seem to markedly contribute to sticking. It is the outstanding object of this invention to overcome the adverse effect of these water-soluble materials upon the surface characteristics of a fibrous board product, such for example as a hardboard, by the novel treatment with water set forth above. It is evident that the exposed surface has the concentration of water-soluble material substantially changed by following this invention inasmuch as there is no sticking or mottling.

I claim:

1. In a process for forming a fibrous board product by pressing a dried mat of lignocellulose fibers wherein water soluble materials are disposed in varying concentrations on the surface of said dried mat the improvement comprising uniformly distributing said water soluble material throughout the surface of said mat, prior to pressing by applying water at a temperature of at least F. to at least one surface of said mat in the ratio of at least 16 pounds of water per 1,000 square feet of surface area of said mat for a period of less than one minute whereby a portion of said water-soluble materials penetrates into a body portion of said mat adjacent the mat surface area being treated; removing surplus water from said mat so as to prevent the formation of pools of water on the mat surface area being treated, and quickly removing the penetrating Water by evaporation at a temperature above about 275 F. before a substantial portion of the penetrating water-soluble material can return to said surface area being treated, whereby said substantial portion remains in the adjacent body portion of said mat.

2. The process of claim 1 in which the step of applying water is carried out by passing the mat into a pool of water.

3. The process of claim 1 in which water is applied to only one planar surface of said mat.

4. The process of claim 1 in which water is applied by spraying water onto the surface area of the mat being treated.

5. The process of claim 1 in which the depth of penetration of said watersoluble materials is .005 inch to .02 inch.

6. A product of the process of claim 1.

References Cited UNITED STATES PATENTS 1,821,209 9/1931 Darrah 162-204 X 2,356,285 8/1944 Street 162-201 X 2,802,403 8/1957 Boehm 162206 FOREIGN PATENTS 652,306 11/1962 Canada.

S. LEON BASHORE, Primary Examiner R. D. BAJEFSKY, Assistant Examiner US. Cl. X.R. 

